1) Field of the Invention
The present invention relates to a novel 4-carbonyl-substituted coumarin compound, and more particularly relates to a 4-carbonyl-substituted coumarin compound which provides a novel photosensitizer for use in photosetting resins.
2) Description of the Related Art
In the field of information recording using a photopolymerization reaction, it has recently been investigated to replace conventional recording methods from a film copy through ultraviolet rays with a recording system for directly outputting through laser beams an intact original which is electronically edited with a computer. However, many sources which are generally used today for radiating high output and stable laser beams have a wavelength output in the visible region as observed in argon laser beams. Conventionally used sensitizing agents for ultraviolet rays cannot be employed because of low sensitivity in the visible region. Addition of pyrylium salts or thiapyrylium salts can improve the sensitivity in the visible region. On the other hand, the addition of such salts deteriorates the stability of a photosensitive layer over time. These salts have hence been difficult to use.
Conventionally, 7-alkylaminocoumarin derivatives have a maximum absorption wavelength of from 400 to 450 nm in the case of 4-unsubstituted derivatives. However, many laser beams which are generally used have longer wavelengths than the above range and thus satisfactory sensitivity cannot be obtained in many cases.
For example, 7-diethylamino-3-benzothiazoylcoumarin and 3,3'-carbonylbis(7-diethylaminocoumarin) have a maximum absorption wavelength of about 450 nm, which wavelength is from 30 to 40 nm shorter than 488 nm of argon laser beams. These compounds still have room for improving sensitivity. Since a positive correlation is set up in a certain range between the content of the sensitizer in the resin and the sensitivity obtained, it is desired to form a stable solution of the sensitizer in the resin in the highest concentration within the given range. The above two compounds have poor solubility and lead to a low sensitizer concentration in the resin. Thus the desired sensitivity cannot be obtained.
The maximum absorption wavelength of these compounds can be shifted to a longer wavelength (hereinafter referred to simply as long wave shift) by converting the position-4 to a cyano group. However, solubility in the resin or storage stability are impaired in many cases.